TAMR is expected to be one of the future generations of magnetic recording technologies that will enable recording at ˜1-10 Tb/in2 data densities. TAMR involves raising the temperature of a small region of the magnetic medium to near its Curie temperature where both of its coercivity and anisotropy are significantly reduced and magnetic writing becomes easier to achieve even with weak write fields characteristic of small write heads in high recording density schemes. In TAMR, optical power from a laser diode is converted into localized heating in a recording medium during a write process to temporarily reduce the field needed to switch the magnetizations of the medium grains. Thus, with a sharp temperature gradient of TAMR acting alone or in alignment with a high magnetic field gradient, data storage density can be further improved with respect to current state of the art recording technology.
In addition to the components of conventional write heads, a TAMR head includes an optical waveguide (WG), and a plasmon generator (PG) that is also referred to as a near-field transducer. The waveguide serves as an intermediate path to guide light (from a laser diode mounted on the back of a slider) to the PG where the waveguide optical mode couples to the propagating plasmon mode of the PG. After the optical energy is transformed to plasmon energy with energy transmission along the PG, it is concentrated at the medium location where heating is desired. Ideally, the heating spot is correctly aligned with the magnetic field from the write head to realize optimum TAMR performance.
Due to an inherent mode profile mismatch between the laser diode's far-field and the waveguide mode required to excite the near-field transducer, the waveguide's cross-sectional dimensions are commonly varied along the length of the slider so as to improve the coupling efficiency. The portion of the optical waveguide (WG) where the cross-sectional dimension changes along the light's propagation direction is typically called the spot-size converter. The spot-size converter usually includes multiple WG layers stacked on top of each other so that the total stack thickness is on the order of the laser diode spot size (around 1 micron). To achieve lateral confinement of light, the WG layers are tapered in the cross-track direction. For vertical confinement of light, all of the WG layers except the primary waveguide that eventually terminates at the ABS, may be tapered in the cross-track direction to a tip that is recessed from the ABS, and with a small cross-track dimension to force the propagating light mode into the primary WG.
Even with confinement of light by using a spot size converter, a substantial amount of light from the laser diode will not be coupled into the waveguide but will instead travel the length of the slider in weakly confined cladding modes. The unconfined stray light is absorbed by any metal elements such as write pole structures in its path thereby causing thermo-mechanical expansion of the metal structures to produce undesired broad area writer protrusion. This stray light issue is associated with designs where the laser diode is butt coupled (i.e. end-fire coupled) into a spot-size converter waveguide. Part-to-part differences in laser diode to waveguide mounting alignment result in significant part-to-part variability in the amount of stray light and broad area writer protrusion that is induced. Accordingly, writer protrusion becomes an uncontrolled parameter.
Since spot size converters are commonly used in the industry, there is a need for an improved light delivery circuit for TAMR layouts where a laser diode is end-fire coupled into a spot size converter waveguide so that stray light does not lead to writer protrusion. The new design should minimize wear on protruded parts, and improve adhesion between adjoining layers by preventing undesirable stress on write head components. Thus, it is desirable to substantially reduce writer protrusion induced by stray light in order to improve reliability.